When restoration experts at Washington's National Gallery of Art began cleaning up their Renaissance masterpiece The Feast of the Gods, they discovered their "Bellini" is not what it appears to be -- that significant portions were altered and repainted sometime shortly after the master's death. Who would have dared tamper with the great man's work? And why? Experts set about solving the Bellini whodunit through use of X-rays, paint analysis, computer simulations, and other forms of latter-day techno-snoopery.